The present invention relates, in general, to semiconductor packages, and more particularly, to a metal system for a semiconductor package that has a thermal expansion buffer.
Thermal expansion buffers generally have been used in the semiconductor industry. These buffers were used to reduce the effects of thermal expansion mismatches between low coefficient of thermal expansion (CTE) materials such as silicon and high coefficient of thermal expansion (CTE) materials used to construct semiconductor packages such as copper, steel, aluminum, etc. For example, a low CTE silicon die that was attached to a section of high CTE copper could be damaged by the difference of thermal expansion rates between the two materials. Placing an expansion buffer between the silicon and the copper reduced stresses that were placed on the silicon die. The buffer expanded at a rate that was between the expansion rate of silicon and the expansion rate of the package material thereby absorbing most of the stresses that occurred. Often the buffers were coated with a material to eliminate the formation of detrimental intermetallic compounds between the materials used for the buffer and materials used for attaching either the die or the buffer. These coatings often were materials which did not readily form strong bonds with silicon attachment materials. For example, one common configuration was a nickel coated thermal expansion buffer. Common materials, such as silver filled glass, used to bond semiconductor die to semiconductor packages did not readily bond to the nickel coating. Semiconductor die that were attached to these buffers generally experienced bond failures after repeated cycles of thermal expansion.
Additionally, some semiconductor die required a direct connection between the semiconductor die and the package. This was generally provided by a wire that had one end bonded to the semiconductor die and the other end bonded to the thermal expansion buffer. Wires bonded to previous thermal expansion buffers also failed after repeated temperature cycles.
Accordingly, it would be desirable to have a metal attachment system that provides a reliable bond between a semiconductor die, and a thermal expansion buffer, and also provides a reliable attachment for a bonding wire.